1. Field of the Invention
The present invention relates to transfer case assemblies, and more particularly to a transfer case housing made of a single-piece casting.
2. Description of the Prior Art
Transfer cases for four-wheel drive vehicles are well known in the prior art, and serve to transmit torque from an engine or prime mover to a plurality of drive axles to thereby drive front and rear axles of a motor vehicle. Typically, the transfer case comprises an input shaft driven by a vehicle transmission, two output shafts driving front and rear axles and a torque transfer mechanism including, but not limited to, driving and driven sprockets, a clutch device and an endless chain element transmitting input torque to the output shaft driving front wheels in a four-wheel drive mode. In case of a full-time four-wheel drive system, the transfer case does not comprise the clutch device. The transfer case is usually mounted behind and is driven by a transmission. Two shafts normally run from the transfer case: one to the front drive axle and one to the rear drive axle.
Conventionally, the torque transmitting chain is housed in a common compartment defined by a transfer case housing or casing. The casing is typically provided with a lubricating oil bath where the chain is partially immersed. The transfer case casing usually includes a number of pieces made by casting. Currently, the most common is a two-piece casing forming a so-called xe2x80x9cclam-shellxe2x80x9d type of housing. Each half of the clam-shell casing is cast and machined separately, then bolted together. A gasket is inserted between each half of the casing to prevent leakage of lubricating oil therefrom.
Inherent to this practice is a slight misalignment of bearing bores due to tolerance accumulation in the separate machining processes. Also, over the time, the gasket wears out and the lubricating oil tends to leak between the halves of the clam-shell casing. Furthermore, additional costs are associated with the use of two castings, machining steps, the sealing gasket and assembly operation required.
The present invention provides an improved housing assembly for transfer cases of four-wheel drive vehicles.
The housing assembly of the present invention comprises a single-piece casing provided with an access opening for assembling components of the transfer case, and a casing cover member for closing the access opening. The novel transfer case casing of the present invention is manufactured as a single-piece casting wherein bearing bores could be machined into the unitary single-piece casing. Thus, the manufacturing process includes only one casting, instead of two, eliminates the subsequent processes of machining of two halves of the prior art casings and fastening them together, and does not require additional sealing gasket. Moreover, the use of the single-piece casing eliminates the bore misalignment problem and any additional misalignment created by bolting of the two halves of the housing together. Also, the single-piece casing design, by eliminating the clam-shell joint, drastically reduces the undesired oil leakage issues. Furthermore, the single-piece casing improves housing stiffness, transfer case durability and noise, in addition to utilizing fewer parts and requiring less labor in assembly.